The present invention relates to devices for mechanically rotating objects and, in particular, to a modular hydraulically controlled rotary actuator.
Rotary actuators are utilized for a wide range of services wherein it is desirable to selectively rotate one mechanical structure relative to another. For example, actuators of this type are frequently used in the field of robotics to rotate a robotic arm to a preselected angular orientation relative to another part of the robot with a relatively high degree of accuracy.
Rack and pinion type actuators, wherein a slidable and linearly movable rack drives a pinion gear which effectively operates as a rotary drive, have been popular and are used in many different types of equipment. Such rack and pinion actuators have many desirable characteristics which include a relatively high mechanical efficiency, low internal hydraulic leakage which allows the actuator to be hydrostatically locked, tolerance for relatively heavy radial and axial shaft loading due to the ability to use relatively large bearings and the availability of a large variety of seals and materials of construction.
The major disadvantage of conventional rack and pinion type rotary actuators is that a cylinder barrel, or the like, is required for providing a pathway within which the racks must travel and this barrel must extend generally outward from a tangent of the pinion gear. Such cylinder barrels are relatively small for actuators requiring only a relatively small torque to be applied to the pinion gear. However, as the torque applied to the pinion gear increases, the length of the cylinder barrel must also increase.
In particular, the conventional method of increasing the torque applied to a pinion gear is to increase the force applied by a single rack acting on the pinion gear or by a pair of opposed racks acting upon the single pinion gear. However, this force cannot be substantially increased beyond a given degree without major modification of the device. That is, as the maximum torque required to be transmitted to the pinion gear increases, the gear teeth must be increased in size to keep the teeth from being broken from the gear.
However, when the teeth are increased in size, in order to allow the teeth to mesh smoothly to provide for a smooth rolling action, the diametral pitch of the pinion gear must be increased in size also. Effectively, this means that the pinion gear must have a substantially larger diameter than is required for a similar pinion gear transmitting a substantially lower torque. Since the teeth are much larger and further spaced on a larger gear as compared to a smaller gear, the rack must also be proportionately larger as the travel of the rack required to move the pinion gear through a particular angular movement is generally proportional to the diameter of the gear. Consequently, the cylinder barrel for the conventional devices must be much longer for a device transmitting a larger torque than for such a device operating under a lower torque.
Often when a mechanical design calls for a rotary actuator of the type disclosed herein, there is sufficient space available in order to allow extension of the actuator axially but not radially or laterally. Consequently, it is desirable to be able to use axial extension to increase the torque output of such an actuator without substantially increasing the radial extension of the actuator, but this option has not been available in the prior art.
Further, the prior art has failed to provide a rotary actuator of the type described herein which can be easily modified with interchangeable modules to generate the required torque for a particular installation. It is usually desirable to have the overall size of the actuator as small as possible; therefore, it is desirable to have such an actuator that can be sized upward for increased maximum torque in incremental and preferably in stages that increase maximum torque by a generally standard and known amount for each stage or module acting upon a drive shaft.
Prior art actuators normally are available in many sizes to produce various torques, but very few parts of such actuators are interchangeable; therefore, it is further desirable that torque generating modules for the rotary actuators be constructed of the same interchangeable parts and that the modules can simply be added together in a laminated fashion to act upon a single pinion gear or shaft having elongate teeth extending axially therealong and being sized for the number of modules required for the particular installation. Such a device allows the torque to be applied to a single pinion gear or shaft to be spread out along teeth that are substantially elongated and can withstand higher torques when such torques are divided into individual component forces acting upon sections of the teeth.
It is still further desirable to have an actuator of this type wherein the racks move with relatively little internal friction which substantially improves the mechanical efficiency of the device.